This invention relates to a V-ribbed belt used to drive auxiliary automotive machinery, such as a generator, a cooling fan and an oil pump, by motion transmitted from the back of the V-ribbed belt (hereinafter called "belt back-face drive").
V-ribbed belts are characterized such that they combine the advantage of flat belts (flexibility) and the advantage of V-shaped belts (high motion transmission capacity) and have therefore application in the area of driving belts suitable for the operation of automobile auxiliary machinery. A typical V-ribbed belt is made up of a compression rubber layer, an adhesion rubber layer laminated to the upper surface of the compression rubber layer, and tension members fixed in the adhesion rubber layer so as to be held in place by rubber of the adhesion rubber layer and arranged in the direction of the length of the belt. A plurality of grooves with a cross section of vee shape are formed continuously in the lower surface of the compression rubber layer in the belt length direction. A composite of a covering fabric and rubber is coated over the upper surface of the adhesion rubber layer.
In early practice, V-ribbed belts were used such that they were passed, in open-drive manner, around two pulleys, namely a crank pulley and an auxiliary machinery pulley. In recent years, however, the manner in which V-ribbed belts are used has changed. For instance, a flat pulley is employed on the back of a belt to obtain an increase in the angle of contact of the belt with respect to an auxiliary machinery pulley in order that the auxiliary machine pulley may be given sufficient driving force. Further, in view of the layout of engine parts, a flat pulley is mounted to prevent the belt from coming into contact with an engine part.
Japanese Laid-Open Patent Application Publication No. 6-323368 shows a covering fabric-rubber composite. This prior art fabric-rubber composite is made up of a covering fabric, an impregnated rubber introduced into the covering fabric, an upper rubber layer applied onto the upper surface of the covering fabric, a lower rubber layer applied onto the lower surface of the covering fabric, and an adhesive rubber layer applied onto the lower surface of the lower rubber layer and used to provide adhesion of the covering fabric-rubber composite to the upper surface of the adhesion rubber layer. At least the upper rubber layer is composed of a rubber compound superior in abrasion resistance and in conductivity, with a view to achieving both a reduction of the belt back-face abrading and a reduction of the belt back-face viscosity, in other words with a view to providing improvement in abrasion/viscosity resistance.
With luxurization of general automobiles, V-ribbed belt back-face drive is more extensively adopted. In order to achieve a compact engine room, reducing the dimensions of pulleys, together with saving space, is making progress. This, however, results in a considerable rise in engin room atomospheric temperature. The above-described prior art V-ribbed belt may find it difficult to perform belt back-face drive because of being poor in heat crack resistance. Accordingly, there is still room for improvement.